呼图壁储气田充放气引起地下应力变化的地震学观测

The Hutubi gas field is the biggest gas storage field in China with a designed capacity of 10.7 billion cubic meters. As a state key construction project, it is the first large supporting system of the project of natural gas transmission from West to East and plays an important role in natural gas season peak shaving and ensuring gas stably supply. The operations of the gas field will lead to the subsurface medium changes and even cause micro-earthquakes. Monitoring the medium changes surrounding the undergroud gas field to safeguard the production safety and lower the vicinity seismic activity has both important scientific and social significance. In this project, we will use big volume airgun source and the assorted three-dimensional observation system to monitor the medium nearby the underground gas field for a long time. Followed researches will be carried out: 1. Quantify the relationship between the subsurface stress changes caused by the gas field production and the velocity changes of the medium. 2. Confirm the sphere of gas field influence and assess the seismicity around the gas field. 3. Build a geophysics model about gas-draw and gas-injection processes and explain the mechanism of the medium changing. Discuss the subsurface medium properties under continuous stress loading and unloading conditions. This project can provide a clear view of human-induced subsurface changes and help us quantitatively understand the relationship between seismic data and underground changes. The results obtained by this project will be very significative to understand the Earth's internal dynamics and ensure the gas field normal operation and have guidance function in shale gas exploitation.

呼图壁储气田是我国目前最大储气库，设计库容为107亿立方米。作为国家重点建设项目，它是西气东输管网首个大型配套系统，对天然气季节调峰及保障平稳供气具有重要作用。储气田的日常运营会导致可观的地下应力变化，甚至诱发微地震。故监测储气田地下介质变化，对保障气库安全生产和评估储气库周边地震危险性具有重要的意义。本项目将利用大容量气枪震源与新颖的立体化观测系统（地面流动台站测线与井下地震计）对呼图壁储气田地下介质进行长期的监测。开展研究如下：1，确定储气田充放气与地下介质波速变化间的关系；2确定储气田生产活动的作用范围及对周边地震活动性的影响；3，建立储气田充放气引起地下介质变化的物理模型，探讨地下介质在重复的应力加载与卸载条件下的变化性质。本项目的开展对认识地球内部的动态过程，保障地下储气库的安全运行具有重要的意义，对页岩气开采等工作具有重要指导作用。

呼图壁储气库是我国目前最大的地下储气库，储气库的注采气作业，会使地下孔隙压力和应力分布会发生较大变化。呼图壁气枪震源与储气库相距约30公里，是非常适合进行地下介质变化监测的人工震源，二者形成了一个进行地震学研究绝佳组合。本研究利用呼图壁大容量气枪震源，结合背景噪声和微地震检测等方法，对储气库注采气引起地下应力变化进行了观测，开展研究如下：1，利用呼图壁气枪震源结合背景噪声方法，对储气库区域的地下介质波速变化进行连续、高精度监测，并成功监测到了气枪震源信号到时变化与气井油压变化的一致性关系；2，利用微地震监测的方法，对储气库周边微地震的活动性进行了研究，并分析了其与储气库生产活动的关系，找出了储气库作业引起周边小地震活动的科学依据；3，利用有限元方法，建立了储气库充放气引起地下介质变化的物理模型，并结合实际注采作业参数，对储气库安全生产提出了建议。本项目的开展对认识地下介质波速随地下应力加载、卸载变化的规律，大型储气库对周边地区地震安全性的影响等方面有重要意义。